Occupant restraint systems with as bags, frequently also referred to as airbags, which are automatically inflated in the case of a serious accident are nowadays installed in a plurality of passenger cars both on the driver""s side and on the passenger""s side in order to possibly avoid, in the case of a serious frontal impact of the vehicle, potential head and chest injuries of the vehicle occupants which are seated in the front. Such systems which essentially consist of a mostly pyrotechnical gas generator and a gas bag as well as of the associated control electronics are increasingly employed in the lateral area of passenger cars in order to dampen and distribute the forces acting upon the vehicle in the case of a side impact over a larger area and thus decrease the injury hazard for the vehicle occupant who is seated on the impact side. Such laterally arranged impact protection systems with gas bag, which are also referred to as sidebags, are for example, accommodated in the vehicle doors or in the backrests.
On the basis of the predominantly positive experience gained with such impact protection systems which comprise a gas bag the trend exists to employ such systems on a wider scale in trucks and buses as well.
Depending on the task which an occupant restrain system of the initially mentioned type is to fulfill, the gas bag in its inflated state must have a precisely defined shape in order to achieve the optimum effect. The so-called driver airbags in their inflated state are, for example, approximately balloon-shaped, while the so-called passenger airbags in their inflated state are approximately cushion-shaped. Side airbags in turn frequently still have intricate shapes in order to be able to comply with the requirements imposed on them.
In addition, gas bags must fulfill two contradictory requirements: On the one hand they must be inflatable as rapidly as possible when required; on the other hand they have to provide as large a distance as possible between the vehicle occupant to be protected and the object with which the vehicle occupant must not collide. While the first requirement calls for a small gas bag volume, a relatively large gas bag volume is the result of the second requirement. The existence of impact protection systems with a gas bag, however, is only justified if their protective effect is as good as possible so that nowadays large gas bag volumes are preferred in order to achieve an optimum protective effect.
Conventional gas bags consist of two or more individual textile parts which are cut from textile flat material and subsequently sewn together. Accordingly, two circularly made-up two-dimensional textile parts are generally sewn together for a driver""s airbag. Upon inflating these conventionally manufactured gas bags into their three-dimensional state which they must assume in order to achieve the desired protective effect, creases occur in particular in the seam area, which extend perpendicular to the seams. These creases result in high stress peaks in the seam area which is already weakened by the seam. In order to avoid bursting of the gas bag in the seam area under load, very heavy fabrics are used in the manufacture of the gas bag. These heavy fabrics in conjunction with the relatively large gas bag volume selected for achieving a good protective effect result in conventional gas bags being relatively heavy. In order to nevertheless ensure the rapid inflation when necessary, larger gas generators have to be employed which are capable of correspondingly rapidly accelerating the relatively large mass of the gas bag. Large pyrotechnical gas generators in turn are disadvantageous in that during inflation the temperature of the gas developed by the gas generator reaches very high values and that these high temperatures can affect the gas bag and destroy its fabric. In addition, a gas bag with a larger mass unfolds only later due to its higher inertia so that the hot gases developed by the gas generator act longer on the still folded fabric which is located near the gas generator. In order to not destroy the gas bag fabric as a result of this bombardment with the combustion gases great yarn thicknesses (approx. 250 to 700 dtex) are employed which ensure that the fabric does not fail even then when glowing particles impinge on the fabric and individual threads start melting.
The relatively large mass of conventional gas bags must, of course, not only be accelerated but also stopped again at the end of the inflation process. In this case, too, great loads occur in particular in the seam area which must be compensated by correspondingly reinforced sears or by multiple seams. These measures again result in an increase in the gas bag weight.
The conventionally used heavy fabrics not only have dynamic disadvantages but, in addition, enforce a relatively large packing volume due to the fact that they are also mostly relatively rigid. The seam areas are naturally particularly rigid and can therefore cause undesired injuries such as, for example, skin grazes of the occupant to be protected if the occupant assumes a so-called cut-of-position attitude while the gas bag unfolds. Any attitude which does not correspond to the optimum position relative to the gas bag is technically termed xe2x80x9cout-of-positionxe2x80x9d, for example an occupant who is seated too close to the gas bag or lateral to it. In such out-of-position attitudes the risk to be fully hit by a rigid seam area is particularly high.
In order to fulfill its protective function the gas bag must comply with two additional and also contradictory requirements. As already mentioned it must be inflatable as rapidly as possible. This requirement can generally be met only with a very tight gas bag because only then will it be ensured that the gas developed by the gas generator is completely used for inflating. On the other hand, the gas bag in the inflated state must dampen the impact of an occupant of the vehicle. To this end the gas bag must allow a defined venting of its gas filling because otherwise the colliding occupant would bounce back. Therefore, in the side facing away from the vehicle occupant, conventional gas bags are provided with openings which can have a diameter of up to 50 mm. These openings are also referred to as xe2x80x9cventsxe2x80x9d. Because these openings are not closed during inflation, a considerable portion of the gas developed by the gas generator escapes so that the gas generator must have a correspondingly more powerful, i.e. larger, design in order to be able to reliably inflate the gas bag. Large gas generators, however, result in the above already explained thermal stresses of the gas bag fabric.
Finally, the conventionally employed heavy fabrics are not particularly tight because of the relatively great yarn thicknesses used so that these fabrics must generally be additionally coated in order to obtain the required tightness. The coatings, however, often have the problem of a poor aging stability so that the satisfactory function of the gas bag might possibly no longer be ensured after many years.
Although known impact protection systems with gas bags decisively improve the occupants"" safety, thus justifying their increasingly large-scale use, these systems still have quite a number of drawbacks which prevent an even better protective effect and moreover increase the manufacturing costs of conventional systems.
The invention is based on the object to improve conventional impact protection systems with gas bags in such a manner that with an increased protective effect as many of the above mentioned problems as possible are solved.
According to the invention this object is solved by an inflatable gas bag for an occupant restraint system, which consists of a multilayered textile composite material which comprises at least one layer of a textile material and one layer of a polymer material whose melting range is lower than the melting range of the textile material, with the textile composite material being formed into a predetermined three-dimensional shape which is to develop during inflation of the gas bag and the individual layers of the textile composite material have been joined together only in the three-dimensional shape of the gas bag.
The gas bag according to the invention therefore differs quite essentially from the previously known gas bags: During its manufacture it is already formed into the three-dimensional shape which it is to assume in the inflated state. The inventive gas bag is heat set in this three-dimensional shape by means of thermal treatment. Contrary to conventional gas bags which are combined or sewn together, respectively, from two-dimensional flat members, the described crease formation no longer occurs during inflation of the inventive gas bag, which in conventional gas bags causes dangerous stress peaks.
Due to the fact that the inventive gas bag is formed into its three-dimensional functional state during manufacture, the strength of its material can be selected considerably lower compared to the previously employed materials because the stress distribution in the gas bag material of a gas bag according to the invention is much more uniform. According to the invention considerably more lightweight textiles can thus be employed as gas bag material. In addition to the previously described advantage of a more uniform stress distribution, forming the inventive gas bag into its three-dimensional functional state during manufacture also makes it possible to reduce the gas bag volume as compared to conventional gas bags having the same protective effect because a gas bag according to the invention can, for example, be preformed into an egg-shaped configuration and in this manner bridge the same distance for which a ball-shaped gas bag with a correspondingly larger volume is conventionally required.
The inventive use of a multilayered textile composite material results in further advantages: The now employable textile materials of lighter weight need no longer be coated but rather obtain their tightness by means of the layer of polymer material which is but joined with the layer(s) of textile material in the desired three-dimensional shape of the gas bag. By means of suitable temperature control during the joining process the resulting textile composite material can also be given a defined gas permeability which can even be adjusted so as to be locally different. For example, on the side of the gas bag facing away from the occupant areas with a higher gas permeability can be generated so that the conventional vent orifices can be dispensed with. Due to the omission of the conventional vent orifices, the inflation losses of the gas bag according to the invention are, on the one hand, much smaller so that the use of a smaller gas generator becomes possible and, on the other hand, the weight of the gas bag is again reduced because the conventional vent orifices are seamed by one or several seams for stability reasons.
Furthermore the inflation dynamics of the gas bag according to the invention can be influenced by a locally different adjustment of the permeability of the textile composite material, i.e. the shape can be precisely controlled during inflation. Thereby, for example, the previously occurring and undesired xe2x80x9cmushroomingxe2x80x9d (mushroom-type ejection of the gas bag in the initial phase of the inflation process) can be prevented. Restraining straps within the gas bag as were previously employed to prevent xe2x80x9cmushroomingxe2x80x9d can be dispensed with in the inventive gas bag, which again makes same more lightweight. The precisely definable permeability of the textile composite material employed according to the invention additionally permits a controlled venting of the inflated gas bag and thus a nearly linear damping of the motion of the colliding occupant. In other words, the inventive gas bag can be imparted an accurately defined deformation energy absorption.
In summary, the inventive gas bag even in its simplest configuration offers the following advantages:
While the previously used gas bag fabrics, e.g. for a gas bag on the driver""s side, have masses per unit area ranging from approx. 180 g/m2xe2x88x92-to 220 g/m2xe2x88x92-, the multilayered textile composite material used according to the invention in the molded state has a 30 to 50 percent lower mass per unit area.
While the previously used gas bag fabrics have tensile strengths ranging from approx. 1,800 to 2,200 N/5 cm (to DIN 53875, Part 1) the multilayered textile composite material of the inventive gas bag is required to have only approx. 25 to 50 percent of this tensile strength.
While the previously employed yarn thicknesses amount to approx. 250 to 700 dtex the yarn thicknesses of the textile material employed for the inventive gas bag may range from approx. 20 to approx. 40 dtex.
The gas bag according to the invention can be brought into any shape which is desired from the point of view of safety while at the same time minimizing its volume.
Due to its superior design the gas bag according to the invention is generally considerably more lightweight than previous gas bags and thus permits the use of smaller gas generators.
The gas bag according to the invention requires a considerably lower packing volume which, for example, allows the vehicle manufacturers to accommodate gas bags with large volumes also in smaller visually more attractive steering wheel hubs as are generally used in sports steering wheels.
According to a preferred configuration in terms of manufacture and function the inventive gas bag consists of several portions each of which is formed into one part each of the three-dimensional shape of the gas bag and which are joined together in the three-dimensional shape of the gas bag, in particular by lap sealing. According to this configuration a gas bag intended for the driver""s side is preferably formed by combining two e.g. approximately hemispherical portions. Such a configuration permits the use of a textile material for the side of the gas bag facing the occupant which is different from that facing away from the occupant so that an optimum adaptation of the textile material to different requirements can be effected. In order to join the individual partial portions, all known joining techniques (with or without an inserted auxiliary tape) can generally be used. The individual portions can also be glued or sewn together. The latter type of joining, however, is the one considered the least advantageous.
The layer of a polymer material provided according to the invention can be constituted by a plastic film or by a plastic fleece. The layer of polymer material itself can consist of several layers, for example, of two thin layers of a melting adhesive between which a plastic film is arranged. The layers of melting adhesive can, in turn, be formed by thin fleeces (so-called hotmelt fleece). With a multilayered structure of this type of the polymer material layer the joint area remains soft and flexible also after hot sealing because the central layer of the polymer material need not be heated to the flow condition. Instead, only the thin melting adhesive layers are heated to the flow condition and provide for the desired intimate interconnection of the textile composite material.
According to a particularly preferred embodiment of the inventive gas bag the textile composite material comprises at least two layers of textile material between which the layer of polymer material is arranged. This embodiment makes it possible to select the textile material on the gas bag inner surface different from the textile material on the gas bag outer surface and, thus, to better adapt it to the different requirements (inner surface temperature resistance, outer surface softness, etc.), In addition, this embodiment also makes it possible to make the properties of the inventive textile composite material more isotropic by joining together the two layers of textile material with an opposite twist at a defined angle in order to compensate, for example, the biaxial elongation differences. It goes without saying that also three or more layers of textile material can be used in order to achieve an even better isotropy. One layer of polymer material is always arranged between two layers each of textile material. In order to achieve a better isotropy the individual layers of textile material need not consist of different materials, but may, of course, consist of the same textile material.
In the case of the inventive gas sag, a knitted fabric, a warp-knitted fabric, or a woven fabric can be used. Preferably, however, knitted fabrics, i.e. warp-knitted or knitted fabrics, are used because with knitted fabrics a very good isotropy can be achieved in the three-dimensional functional state of the gas bag, even in the case of only a few textile layers. Woven fabrics, however, always have a warp and weft direction so that a high isotropy is difficult to obtain.
In order to facilitate recycling of the gas bag according to the invention, the layers of textile material and the polymer material preferably consist of the same material, for example, of polyamide or of polyester.
The initially mentioned problems of conventional impact protection systems with gas bags are also solved by an inventive method for the manufacture of an inflatable gas bag, wherein a layered structure of at least ore layer of textile material and one layer of polymer material whose melting range is lower than the melting range of the textile material is brought into the desired three-dimensional shape which develops on inflation of the gas bag or a portion of said shape by means of heated forming tools and is thermally set in this state and simultaneously laminated to a textile composite material. This method is particularly well suited for the manufacture of a previously described inventive gas bag.
In the manufacturing method according to the invention the layered structure whose layers are not yet securely joined to one another is brought into the desired three-dimensional shape which may correspond to the complete gas bag or to a portion therefrom between usually two heated forming tools and is thermally set in this state and simultaneously laminated to a textile composite material. The method according to the invention is thus a three-dimensional textile laminating and molding method. In the inventive manufacturing method for gas bags it must be ensured that no excessive compacting pressure is generated between the forming tools so that the generating textile composite material maintains its textile properties as far as possible.
The thermal setting of the obtained three-dimensional shape is effected by selecting the temperature of the forming tools such that the textile material does not begin to melt or is damaged but is thermally set in the desired three-dimensional shape. If required, thermal setting-can be assisted by chemical auxiliary agents and/or mechanical rubbing movements of the forming tools. Due to the laminate generated in this manner the textile composite material of the gas bag according to the invention has an extremely high strength with a low weight. The mass per unit area of the employed textile composite material in the three-dimensional functional state preferably ranges from approx. 100 g/m2 to approx. 150 g/m2.
According to the invention, melting starts only with the layer of polymer material in order to achieve an intimate connection with the textile layer or the textile layers. The commencement of melting of the polymer layer can be controlled in such a manner that, at the same time, the permeability of the generating textile composite material is accurately adjusted. The temperature can thereby be controlled in a locally different manner so that locally different gas permeabilities can be obtained. In addition to or as an alternative to the possibility of adjusting the gas permeability of the gas bag by means of controlling the temperature in the inventive manufacturing method, it is also possible to perform a specific mechanical perforation of the layered structure or the generating textile composite material, e.g. by means or a forming tool provided with needles, during the forming, heat setting and laminating process.
If the gas bag is to be combined from several portions, these individual portions are joined together in the manufacturing method according to the invention in the desired three-dimensional shape, preferably by means of lap sealing. Compared to the previously used sewing technique which yields a maximum of 50 to 60 percent of the fabric strength in the seam areas; at least almost the strength of the remaining textile composite material is achieved also in the joint areas by means of lap sealing. This leads to a significant weight saving for a gas bag which is manufactured in accordance with the inventive method. In addition, the edges of the individual portions of the gas bag which are manufactured in accordance with the inventive method can be exactly seamed with the seam not extending outwardly or inwardly as hitherto but being flush with the three-dimensional shape of the gas bag. Therefore, no protruding seam is generated when joining the individual portions but the joint area is also located within the enveloping surface of the gas bag. In this manner a precise lap sealing of individual portions becomes possible. In addition a joint obtained by lap sealing is stronger and more lightweight than a conventional sewn seam.
The inventive manufacturing method permits the individual textile layers to be stretched during the forming process up to an also locally defined residual elasticity. As already explained in conjunction with the above described gas bag according to the invention the inflation dynamics can thereby be precisely influenced. Moreover, stretching of the textile layer results in an increase of the tensile strength of the textile composite material.
The inventive manufacturing method can be carried out with textile materials made from all commercially available synthetic fibres but also with textile materials from natural fibres, e.g. mercerized cotton. It is of importance that the melting range of the polymer layer(s) is lower, preferably only slightly lower, than the melting range of the textile material. A number of successful test samples has already been manufactured both from polyamide and from polyester textile materials. In general, such textile materials have a melting range from approx. 210 to 240xc2x0 C. The temperature to be selected in the inventive manufacturing method when using such textile materials is therefore within a range of between approx. 180 and 210xc2x0 C. so that the textile material will not be damaged, the polymer material layer, however just begins to melt.
The above described gas bags with their advantageous properties can be manufactured by means of the inventive method. In spite of the generation of a multilayered textile composite material the manufacturing costs are, due to the significantly lower mass per unit area, considerably lower than the manufacturing costs for conventional gas bags which must use the heavier textile materials.
Although the just described manufacturing method has been explained above with reference to gas bags for impact protection systems, it is obvious for those skilled in the art that this manufacturing method can very advantageously be employed for other formed parts made from textile materials as well. For example, textile formed parts can be manufactured for work, sports, leisure clothing or for containers of textile materials such as rucksacks or bags. One sample application so would be to make clothing shoulder sections which are to be rainproof but breathing by means of the inventive method. In this manner the hitherto seam on the shoulder which leads to tightness problems or which has to be sealed separately with a considerable amount of effort can be omitted. The method according to the invention is therefore particularly suited for the manufacture of formed textile parts which are to be permeable for water vapour in one direction in order to be able to emit the water vapor which is generated when sweating during heavy physical labor and waterproof in the other direction in order to provide, for example, a protection against rain.